Anxious as he was to get moving, Leslie Groves
decided to make one final quality control check. On November 18,
1942, Groves appointed Warren K. Lewis of the Massachusetts Institute
of
Technology to head a final review committee, comprised of himself and
three
DuPont representatives. During the final two weeks of November,
the
committee traveled from New York to Chicago
to Berkeley and back again through
Chicago. It endorsed the work on gaseous
diffusion at Columbia,
though it made
some organizational recommendations; in fact, the Lewis committee
advocated
elevating gaseous diffusion to first priority and expressed
reservations about
the electromagnetic program
despite an
impassioned presentation by Ernest
Lawrence in
Berkeley. Upon returning to Chicago, Crawford H. Greenewalt, a
member of
the Lewis committee, was present at Stagg Field when CP-1
(Chicago Pile #1) first went critical. (For more on CP-1,
skip ahead to "Early Pile Design, 1942.")
Significant as this moment was in the history of physics, it came after
the Lewis committee endorsed moving piles to the pilot
stage and one day after Groves instructed DuPont to move into pile
design and construction.

The S-1 Executive Committee
(left) met to consider the Lewis report on December 9,
1942. Most of the morning session was spent evaluating the
controversial
recommendation that only a small electromagnetic plant be built.
Lewis and
his colleagues based their recommendation on the belief that Lawrence
could not
produce enough uranium-235 to be of military significance. But
since Lawrence's calutrons could provide enriched samples quickly,
the committee supported the
construction of a small electromagnetic plant. James Conant disagreed with
the Lewis committee's assessment, believing that uranium had more
weapon
potential than plutonium. And since he knew that gaseous
diffusion could
not provide any enriched uranium until the gaseous diffusion plant was
in full
operation, he supported the one method that might, if all went well,
produce
enough uranium to build a bomb in 1944. During the afternoon, the
S-1
Executive Committee went over a draft Groves had prepared for Vannevar
Bush to send to President
Franklin D. Roosevelt.
The draft supported the Lewis committee's report except that it
recommended skipping
the pilot plant stage for the pile. After Conant and the Lewis
committee
met on December 10 and reached a compromise on an intermediate-scale
electromagnetic
plant, Groves's draft was amended and forwarded to Bush.

On December 28,
1942, President Roosevelt approved what
ultimately became a government investment in excess of $2 billion, $0.5
billion
of which was itemized in Bush's report submitted on December 16.
The
Manhattan Project was authorized to build full-scale gaseous diffusion
and
plutonium plants and the compromise electromagnetic plant, as well as
heavy
water production facilities. In his report, Bush reaffirmed
his belief
that bombs possibly could be produced during the first half of 1945 but
cautioned that an earlier delivery was unlikely. No schedule
could
guarantee that the United States would overtake Germany in the race for
the
bomb, but by the beginning of 1943 the Manhattan Project had the
complete
support of President Roosevelt and the military leadership, the
services of some
of the nation's most distinguished scientists, and a sense of urgency
driven by
fear. Much had been achieved in the year between Pearl Harbor and
the end
of 1942.

No
single decision created the American atomic bomb project.
Roosevelt's December 28 decision was almost inevitable in light of
numerous earlier
ones that, in incremental fashion, committed the United States to the
pursuit of atomic weapons. In fact, the essential pieces were in
place when Roosevelt
approved Bush's November 9, 1941 report on January 19, 1942
(left). At
that time, there was a science organization at the highest level of the
federal
government and a Top Policy Group with direct access to the
President.
Funds were authorized, and the participation of the Corps of Engineers
had been
approved in principle. In addition, the country was at war and
its
scientific leadership -- as well as its President -- had the belief,
born of the
MAUD Report, that the project could result in a significant
contribution
to the war effort. Roosevelt's approval of $500 million in late
December
1942 was a step that followed directly from the commitments made in
January of
that year and stemmed logically from the President's earliest tentative
decisions in late 1939.